Paramagnetic gas analyzer



y 22, 1952 R. s. MEDLOCK' 2,503,965

PARAMAGNETIC GAS ANALYZER Filed April 2, 1949 2 SHEETS-SHEE'1' 1 Fig.l

INVENTOR. REGINALD. STUART MEDLOCK ATTORNEYS July 22, 1952 R. s. MEDLOCK PARAMAGNETIC GAS ANALYZER Filed April 2, 1949 2 SHEETS-SHEET 2 TSI INVENTOR. REGINALD STUART MEDLOCK 'WMMM@% ATTORNEYS Patented July 22, 1952 UNITED STATES OF CE a -i 1 f V PARAMAGNETIC assuming-zen Reginald S.= Medlocln Luto n;v Englan di fass to Leeds and Northrup Company Phi I Pa., a,corporation Application April 2, 1949,:Serial No.18

' t In Great Britain October l Claims. (01.3

This invention relates to apparatus for a ssessing the amount of. a .gas of relatively high magnetic, susceptibility contained in a mixture" The primary, thoughnot exclusive,

of. gases. v application of. the .invention is to the assessing otthe oxygen content of gas; mixtures.-

Oxygen; has; a magnetic susceptibility much greater thanthat of any other gas except nitric oxide and closely obeys theCurie; law according to .whichsusceptibility varies inversely with ab solute-temperature. This fact has been utilized in known apparatus for assessing oxygen content.

'; The-invention is illustrated in and explained inzconnection: with the accompanying drawings in;which Figures 1 and2 show a knownapparatus, Figure 1 being a schematic representation of the general arrangement and Figure 2 being a diagrammatic view showing the cell A, bridge and-connections; while Figure 3 is a diagramm'atic. representation of one embodiment of the invention; and'Figure 4 is a diagrammatic representation of a modification. 1 v 1.

In order. :that the inventionmay be the better. understood .a' known oxygen content assessing apparatus. utilising the above general principle will firstbeidescribed with reference to Figures land-2..." 1.. In thezknqwn apparatus of Figures-1 and the gas-is passedthrough an analysis cell generally designated 1} and consisting of a cylindrical housing A] which a concentric central pormenu whic th the hw i ade s nan uw ar; space o ,flo -g an lcmz, e gas to be tested; n e the an la space th ou i s heist; ing wall at A4 at one end of a diameter and le vesthe housing at A5 atthe opposite end of said diameter so thatthere are twoequal and similar gas paths one each side of the central portion asuindicated by the arrows in Figure 2. Diametrically across the central portion is a horizontally arranged cross-tube AB whose length is at right angles to the diameter on which the entryand exit ports for the gas are positioned, said tubecommunicating at both ends-withthe annular space A3. On the tube is wound a suitable heater winding A! which is symmetrically r apsedther m and is vid d with endgoni nect ionsnt niiand a centre tap connection All). whole analy sis cell is mounted between the polepiecesBl. B2 oi a permanent or other magnet sys't eni 133 (see Figure 1)' and'the said pole pieces and the central portion of the cell are soarraniged that the magnetic flux, which passes atright anglestothe length of thetubeAli and to.

l qr d 1 1 I in one-half' ionly of th central portion f -the 9-5 n F h s, h s nd ca e o ventionally byedotted shading. I [notherwords, the arrangement is such that practically yall; the

. magnetic flux passes through the centralfportion ofutheicell to one sidel'in Figure 2 theright hand. side). o'fthefdi'ameter onwhich the entryand exit p'prtsmr the gas are situated; thefother half, oflthe central portionzcarrying as nearly as pQssible" 'z'erd flux 'or. at any 'rata only unavoidable. leakage The two. halves.- of the heai' ing winding on eithefside' of the centre tap-are asso; ciated with a resistancebridge or the like in y convenient way. .For example; .as indicated in.

Figure 2. the ends A8, A9 of thewinding maybe:

connectedftc theopposite ends of 'a' resistance consistingbf' equal'elements'Rl R2 across-which a .potentialis applied, from any convenintjsuitablesou'rce s, the middle point P between the r e sistance elements being connected througha' gal-1f vanometer .Gto'. the centre tapAl O.

vWithjthisflarrangement' when'g'gas is p sed through the cellan'd currenttis fed to 'the'hating winding the portion of the gas'in-thehorizpntal tubeAii will become heated and; if it contains. oxygenlitsmagnetic susceptibility will decrease there. J In consequence there will be a tendency fortheunheated gas 'in the annular spaceof thevv cell to be 'aaractea into" the magnet field to disiv place the heatedgas there. The fresh -or displacing gas when it reachesnthe -portion of the tube in the. magnetic field is inturn heated and ii p aced b'y cool gas. Accordingly, a continuous; Ofgas o u si hr s he 1 o izq lta tube; from the half inthe magnetic field to the-half. which out of the magnetic field. e., from-right: to left in Figure 2. If, therefore, the bridge ;is

balanced before. the heating current is switched on itwill become unbalanced to anextent which: depends, among other, things, upon the, oxygen contentof the gas. The degree of: unbalance maybe employed toindicate or recordthe oxygen content or to produce some desired control action in dependence thereon If the gas containswnoj oxygen; there is no tendency for flow withinrthe; tube A6 because themagnetic field is" in suclr case inefiective to induce'fidwof the gas andhe"- causev the ends of. the tube A6 "communicate with regions of the annular space A3 between'which there is no pressure; differential. In brief, the

' rate of fiowof the gas in thermal-transfer rela-- tion to both halves of thetemperature-sensitive: resistor -A'| is a function of the percentage of.

oxygenfin the gas.

the general plane of the cell, concentrated s5 While fanapparatus as above described rs cndsj;

faithfully in dependence upon oxygen content it is unfortunately not dependent only upon oxygen content but also upon the specific heat and viscosity of the gas. It may be shown that in an apparatus as above described the equation defining the E. M. F. developed across the galvanometer or other responsive member of the bridge includes also' the factors of specific heat'of the gas (the E. M. F. is directly proportional to this) and the co-efiicient of'viscosity of the gas (the A!" 3. a I V E. M. F. is inversely proportional to this); cordingly alteration of specific heat or viscosity;

-7 both of which occur with changeof gasteinp'erw;

to the vertical arrangement of the tube-2A6, gas

flow will occur due to convectional effects on heating so that the fiow of gas through the central tube will, be a function of the viscosity of the gas and the temperature difference between the two halves of the heater winding will be a ture and composition, affect calibration "ofthe i" apparatus and such calibration is apt, withknown apparatus, to be diflicult and to require :a good.

deal of careful checking and calculation; The

present invention seeks to avoid these difiiculties 1 According to this invention an apparatus for assessing theamount of a gas of relatively high magneticsusceptibility-fin a" mixture otsasjes and ofthefkind in which the gas is passed through We h rei it shf e t qdq 'a ed ae t e presence of 1a *m n fifl new" in'duce -a--fiow of gas in dependence upon change of js'usceptibility due to heating thereby 'ftd "produce a response in dependence upon "said flow is characterised by the provision ot" correction means wherein the-gas is heated'in-theabsence or a magnetic field so to produce a how independence "upon;the said heating, the spe cifid heat-of the gas and the viscosity thereof and wherein a response is obtained independence upon said flow; the whole arrangement being such that the response due to specific heat "and viscosity in saidcorre'ction means substantially cahcels the response "duetothesame ca ses in th'e'cell; the two-responses being c onfib'in'ed' to produce-amt response "dependent substantially only upon themagnetic su'sceptibi'lityjo'f the gas.

Preferably ei ec fi qn mean co rise a nd cell 'si nilarto the-firstf except that there app d 'masne cfi ldand th the h th'e-gasQ Preferably also the heating in the "cell and nthecolj fiction me nsiis n bd c d v e e f trical' heatingx windings" arrangedtm be diff f en't'ly 'cooled'in'diflerentparts there i indpnd-j er-ice upon the gasflows' theret gh; thereby to produce 'electrica'lf responses? in dependenceuponsaid gas fiows. I V i "It will be seen "that-since "the response "given by thefirst or main cents dependent upon mag-f netie efiect-s, specific heat e'fiects' and viscosity e'fieets' whereas the responsegiven'by the correction means is dependent on spacific"heat" e ffe'cts and "viscosity' effects only; the-net result is that desired name1-y an indication orother Q output dependent upon magnetic effects only.

Eigure 3 shows one'embodiment' of thepresentinvention utilising two cells, namely a first cell, VIA and a reference cell- 2A. l m" Figure" '3 references including the number prefix are -ap-" propriate to one cell (or its circuit) while those appropriate to the other (or its circuitY 'are given the number .prefixQ, the same references (apart from the number prefixes) :beingused-for corresponding parts in Figures 1,2 ami -3 and also, so far as possible, in Figure 4. r

Referring to -Figure- 3 there is employed an analysis cell IA and associated bridge circuit generally as hereinbefore described with time :to Figures 1 'and 2; the appliedyvoltage tor the heating n g b n h w re'rifalt r i instead" ofdire'c t current;

There is function of the specific heat and viscosity of the gasi "In absence of heating of the gas by winding 2A1, there is no tendency for flow within the tube 2A6 since the ends thereof communicate, with regions of the annular flow channel betweemwhich there is no pressure differential. The electrical circuit used, with the two cells is a simple combined bridge circuitn lnz the example' how-n 'a eentre tapped resistance bridge hon,-

s'is ng of the equal elements-1R1,-'lR.2;.?is.:con: nected across the outer terminals lA8,.lA9 (if the heater winding l A1 of "the: first cell i l A and a similarcentre tapped resistanceabridge .comprising the equal elements iRl 2R2 is" connected across the outer terminals ZA B; 2A9 of the heater Windin'g'ZA'I ofthe seconddcell ZAs Altemating current is supplie'd through a -transformer flS- hav'in whi -'is acrossone resistance bridge and the other offivl iich is across the other: "ZI h'ei centre arranged to produce-ta I convectional *flow of V point- -2P- of the-resistance bridge ofsthe second or 're'ferenee cell is-connected to the icentr'e itap-q ping ZA 'I'D of the heating-winding ZA'I- dLthfat cell -through a resistance slide wire SVlh-a moi).-

able t'ap on which is connectedflthrough a gaI-vanometer-G having an field iwinding':

F'W to the centre pcint I A lIi ofthe heating wind-.- ing IA"! of 'the' -first celli l'lhe icentre pointsiljB,

2? of the two resistance' bridges xarexdirectiyconnected together to complete thexoircuit. "Where the arrangement is required .to .eiiect a a control, or operate a re'cordinginstrumentnn the like the movable point onthe slide 'zwirelmay be arranged to be automatically controlie'd bythe galvanometer by any convenientknown :tdll'oweup system (not showm so that: it is automean. v d e'e pr e c i 1? since which maypccuri' S-uc automatic'jmovemen isl-then 'available or ication-of the oxygen-content or for rec'o di {drier-producing the required control action; The gas to -be tested may be passed through one cell 'and then through the re'ference' cell (asin Fig; 3-) -or' a parallel arrangement of the two cellsmay be- It willbs noted that-' with arrang ernen ts inaccordance" with -thi's--i n-vention mizwmcn twdi bridge circuits are employed and the output of one is measured in terms ef the ratio to the output of the other, inherent voaageeompensaaon is ob'tained-an incidentalbut importantprac ticaj d a ae "& V

heinvention is fn otflimited =to the particular apparatus described and other arrangements adapted toprovide compensationforvaria one due to specific heat and viscositymayhe an ployedflFor example; as indicated in 'Fig-ure i, the compensation correction-cell instead of bei ng' similar to the analysis cel-l' comprises a tube- I'-- iorining the sole gas'fpathf'through the co se satingcell 2B and' 'upon whi'ch' is 'a'"ce'n'tre"tapped also pro heati hg'winding 2 associated with-a's c dndhiidge two secondaries TS'I and 'I SZ one Q of as alreadydescribedi-Ffig. 3, as comprising equal elements 2Rl, 2R2 with a centre1p0int2P bet-Weenthem. The'gas reaches tube lvia a length of capillary tube 3 precededzby any convenient known form of. constant'head .pressureregulator schematically indicated at 4 and which accord-. ingly controls the pressure drop across the capillary tube 3 which in turn proportions-the gas flow in accordance with'viscosity. Specific heat ;correction is effectedbyiv-irtue of...the .variation in heat transfer from. one half of the-heating wind ing 2 .to the other '.-:half, ;heat being. applied. in the example -.i1lus trated, from an .A. .C: source through transformerETSe I 'g :-.;Thus1as iii-Fig; 3',- .the gas-.flowithroughzthe compensating. cell is a function; of the viscosity ofvthe gas -.being analyzed and the temperature difierence .betweeni the. two halves of, the-.heater winding, or: paired resistors of the compensating cell, is a function of the specific heatwand' VZ lS'r. cosity.= Inbrief, as: in Fig. 3, the correction cell and its associated bridge circuit produces a response in dependence upon the-specific heat and viscosity of the-gas which substantiallycancels the response due to the same causes in the analysis cell and its bridge circuit so that in consequence the net'response of the twocells and networks'is dependent substantially solely onfth e magnetic susceptibility of the gas;

What is claimed'is; H

l. A system for measuring the concentration in ages, of a component of relatively high magnetic "susceptibility with correction forspecific heat and viscosity of th'e'gas'comprising'two cells for said gas, means for applying heat and magnetism to one of said cells and heat only to the other of said cells to effect in said cells difierent flow rates similarly affected by the specific heat and viscosity of the gas, said heat-applying means comprising electrically heated windings whose resistances respectively vary with changes of the flow rates in said cells, electrical networks respectively including said electrically heated windings and connection with their outputs in opposition, a responsive device in circuit with said networks, and adjustable impedance means connected to effect null response of said device by balancing the output of one of said networks against an adjustable fraction of the output of the other of said networks, the setting of said impedance means at balance being a corrected -measure of the concentration of said component of high magnetic susceptibility and the extent of adjustment between successive balances being a corrected measure of the change in concentration of said component.

2. A system for measuring the concentration in a gas of acomponent of relatively high magnetic susceptibility with correction for specific heat and viscosity of the gas comprising two cells for said gas, means including a magnet and an electrically heated winding for inducing in one of said cells a gas flow dependent upon the magnetic susceptibility, the specific heat and viscosity of the gas, means including an electrically heated winding for inducing in the other of said cells a gas flow dependent upon the specific heat and viscosity of the gas, electrical networks respec.

tively including said electrically heated windings, a source of alternating current for said networks whereby the output of each is an alternating current voltage varying in accordance with the flows in said cells as respectively induced by their aforesaid flow-inducing means, a responsive device in circuit with said networks, and adjustable "impedance means connected to. efiect, null re put of. the network including ;said otherof the cells, the setting of said impedance meansbeing; a corrected measure-of the concentration of said component of high magnetic susceptibility.

33. Asystem for. measuring. the. concentration; in a gas of .acomponentof. relatively .highlmagr netic, susceptibility corrected ,for; variations; in specific-heat and ;viscosity ofthe gas comprising; analysis cell means hayingapairof temperature: sensitive resistors disposedv along a single :path; in. whichthereis no flow-ofgas inabsence of? applied heat ;and magnetism, said pair of resistors. beingincluded-inrbranchespof a circuit to produce. an.1. tput-' si nal. means f r app heat. and magnetismto the gas insaid analysis cellg-rneans, to reflect flowi here f su ssivel -pas s iclresise tors, the resulting temperaturediiference of the resistors; of; said analysis cell means, producing. an output signalmagnitude which is: zerogin, ab, sence of .,said, opmponent and which for; presence.

of-qsaid. component varies ;in, dependence'..upon-.

th ma netic ,s pt b tw-the specific. heat and the viscosity of the. gas, correctiomcell means having a second pair of temperaturepsensitive esis r yd ed alon -.-.a s le flow: path.- .in which there is no now of gas inabsencepf-applied heat, saidsecond-pair of resistors ;being included in other circuit branchesgto ;produce a second.

utput i eans r. p yin .heatin'l the bs nce oimaen tis to h as=.in; id co rec: tion cell means to effect flow thereof successively past the resistors of said second pair, the resulting temperature difference of the resistors of the correction cell means producing a second output signal magnitude which varies in dependence upon the specific heat and viscosity of the gas, and electrical means upon which is impressed the output signals respectively produced by the paired resistors of said analysis cell means and the paired resistors of said correction cell means to provide a resultant which is zero in absence of said component and which in presence of said component is substantially solely dependent upon changes in magnetic susceptibility of the gas.

4. A system as in claim 3 in which the electrical means is in the output circuit of two bridges respectively including the paired resistances of the analysis cell means and the correction cell means and whose unbalances respectively vary with the temperature difference therebetween, said bridges being connected to effect mutual cancellation of 'unbalances due to the specific heat and viscosity of the gas.

5. A system as in claim 3 in which both cell means each has an annular flow-channel for divided flow of the gas and a cross-tube connected to diametrically opposite points of the annular channel with the paired resistors sideby-side along the axis of the cross-tube, theaxes of said cross-tubes being substantially horizontaltien Gen means is a function v of the specific heat. and niscesity o'i-the gas supplied thereto.

appanatus for determining the amount of gas- 6i"- relatively high magnetic susceptibility in-a mixture of gases subject te changes in vise-J cosity anelspecific heat :cdm'pnising means ior supplying: heatingcurrent; a firstelectrical network including temperature-sensitive resistance meanshealted by eurrentfrom said supply means, arr analysis: cell comprising said temperaturesens'itive resistanee nieans anmmeans for ap plying a magnetic iield to the gas mixture thermakti'ansier nelation-to said fesistafncem'ea'ns td-produce a, flow-dependent upon the amount therein 1 of gas efrelatively highmagnetic sus ceptibilitygthe resistance of said resistaneemeans of said analysis cell thereby varyin'g independenee" upon such magnetically I induced flow; the

viscosity andspecificheatcorrespcneiinglytovary the-voltage between output terminalsofsaid network; a second electrical netwbrh including temperature sensitive resistance means heated by current from said supply means, a ccrrecti'cn cell comprisingsaid second-named teni'peif ature-sen'-' siti-ve resistance means, means. fer efieeting fiow ofi said -gas mixture in-the1 'mal-ti ansfen relation" to the mesistan'ce means-bf said correction 0e11,;

themesistanee of said resistance means of the connection CeH-Vaiying in dependene upon-the viscosity and specificheat'eorrespondinglyte vai -y the uoltage between output terminals ef'said sec end-network, a responsive device in circuit with said networks; and impedance means adjustable to eflect null respbnseof said 'gleviceby balancing the outputvoltage of one ef saizinetvi erks against a fraction of'the autput voltage .ofthe other ei said networks, the setting of said impedance means. atbalance being a measure of the @011.- centration of. said gas .of relatively hi h magnetic susceptibility corrected 'for changes in viscosity and specific heat of the gas mixture. 7 v ..8.\An apparatus .as' defined in claim '7 wherein the correction celliissignilar to the analysis cell except'that there is no applied magnetic field..

9. apparatus as defined in claim '7 wherein the-flowlofwthe gas mixture in thermal-transfer relation tothe 'i'esistance means of the correct-v tion cell is effected by heating it in a suhstani tially vertically disposeditube. .7 Y: -10.J'An appar-atus as, defined inclaim 7 wherein the flew of the gas mixture in thenmaletnansfen relation to. the resistance means'of the correction cell is ieffected by a constant; head-'pressure'zrege ulaton andf alconstriction' ibetweenisaid' regulator and the c'el'l." v J j v REGINALD S.MEDLOGKa-.r

V REE BENQES clean The following references "are of: ifiecordin the fileuef this patent:

,7 "UNITED STATES liui be L377 h rry =-.=V-.- ew Mar. 21 3.50

, FOREIGN PATENTS Number," CQuntry pate 

